The crown prince of crime Joker and Harley Quinn have broken up. When she announces this to the world by blowing up the Ace Chemicals family, all hell breaks loose.

The immunity she enjoyed thanks to Joker is gone and everyone in town, or so it seems, is out to kill her for something or the other.

And, then there's Cassandra Cain, the young pickpocket who eats a diamond to hide it from the police. A special diamond which had the secret to a multi-billion dollar treasure. A diamond that belonged to Roman Sionis, the evilest guy in the city at this time. He announces a bounty on Cass. 

Then there's Dinah Lance (aka Black Canary) who has agreed to be a police informant, and is working with Renee Montoya to bring down Sionis. Montoya who is in pain, as her partners have repeatedly taken credit for her work and got a promotion while she has stagnated.

And, then there's also the mysterious Crossbow Killer, who is out killing some high profile people.

Somehow, all their paths cross, as they all stand together against Sionis. Will they survive against his army?